C4 Corvette Radiator Swap - Trending Downward

Engine heat. It's been an operational bête noir in the Corvette world for decades, and it doesn't take an advanced degree in thermodynamics to understand why. Take a big V-8, shoehorn it into the tight engine bay of a slope-nosed performance car, stir in a heaping helping of WOT, and even the best-designed factory cooling system is going to have trouble keeping the temp-gauge needle from twirling toward crimson.

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In the case of our '96 coupe project car, the problem was further exacerbated by our penchant for aftermarket speed hardware. Starting with the installation of a high-stall torque converter, our C4's operating temps have been on an upward trajectory into the danger zone, and the recent addition of a pair of thick-decked TFS cylinder heads helped not even slightly. Factor in the suffocating curtain of ambient heat that descends over central Florida each summer, along with the fourth-gen Vette's, ahem, "unique" approach to airflow management (more on that anon), and it was clear that curative ministrations were in order.

As we've often done in the past, we consulted David Walker of Zip Corvette for a recommendation. After reviewing Zip's arsenal of cooling-system upgrades, Walker sent us an aluminum Direct Fit radiator designed specifically for our C4 (PN RA-170, $499.95). The Direct Fit unit uses a two-row design (as opposed to the factory single-row layout), theoretically doubling cooling capacity, and it features welded aluminum end tanks in place of the crack-prone plastic tanks on the stocker.

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But perhaps the most appealing aspect of the Direct Fit radiator is reflected in its name. Unlike most aftermarket replacements, the Direct Fit is engineered to drop directly into the stock mounting position, with no cutting or fabricating required. In fact, the most time-consuming portion of the installation involves the removal and replacement of the factory shroud, making this a job you really can perform in your driveway or garage in just two to three hours.

You'll note that we said "you" and not "us," since this author's last adventure in cooling-system maintenance ended in minor scalding, major mortification, and a Lake Titicaca–size puddle of antifreeze on the garage floor (don't ask). Embracing our mechanical limitations, we enlisted the services of local Corvette tuner AntiVenom, whose expert techs quickly carried out the job while pretending to still like us. Follow along now as we take you through the process.

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After giving the engine plenty of time to cool off, AntiVenom tech Kyle Miller begins the job by removing the air-intake tract.

Next to go are the shroud bolts. As shown here, the lower/side bolts are somewhat difficult to access, but you should be able to free them using a socket extension and a healthy dose of patience.

With that done, Miller jacks up the car, secures it on jackstands...

...and drains the coolant from the factory radiator.

Once the radiator hoses, fan relays, front air dams, and coolant lines (shown) have been disconnected, it’s time to liberate the shroud and radiator.

Removing the shroud may require a little finagling, as it’s a tight fit and there are numerous lines and bits of engine hardware hindering its egress.

Take your time and work it out, bit by bit, until it’s free.

Because of its design layout, the C4 Vette snorts more questionable stuff up its schnoz than all the cast members of Celebrity Rehab combined. As you can see here, much of it ends up on the radiator and A/C condenser, where it can block the flow of cooling air. Yank the shroud and clean the crud from these pieces at least once a year to keep your system in top operating condition.

The stock radiator should slide out with a minimum of effort. With it out of the way, Miller took the opportunity to de-gunk the condenser with compressed air.

This side-by-side photo helps illustrate the advantages of the Zip Direct Fit radiator (left) as compared with the stock C4 unit. The additional thickness of the Zip piece is attributable to its two-row design, which effectively doubles cooling capacity. Also note the precision-welded aluminum neck and end tank, which are virtually immune to cracking.

Prior to installation, Miller secures the included adhesive-backed foam seals to the top and bottom surfaces of the radiator. These ensure that all incoming air is directed across the radiator’s cooling fins.

As promised, the Direct Fit radiator dropped right into place.

We did have to slightly trim two of the shroud’s mounting tabs to accommodate the burly Zip unit.

The plus-size Direct Fit unit also pushes the shroud slightly rearward, creating a small gap between it and the radiator.

Not to worry: The kit comes with a heavy-duty plastic shim that plugs the opening to create a good seal.

After reinstalling the various lines and hoses, Miller uses a specialized tool to create a vacuum in the cooling system...

...then refills the system with fresh coolant. If you don’t have one of these tools, you’ll need to bleed any remaining air using the factory “weep” holes. Consult your owner’s manual for the proper procedure, and be sure to use a coolant that meets GM standard 6277M.

With the Direct Fit radiator installed, the engine bay is virtually indistinguishable from stock. We did, however, immediately notice a marked improvement in cooling under comparable conditions. In our pseudo-scientific test loop through the Tampa exurbs, coolant temps topped out at a high of 185 degrees (F) on a 75 degree day, down from a max of almost 200 with the stock unit. That reduction should translate directly into improved engine performance and increased component life, making this one upgrade that’s well worth the investment.